This invention relates to a microwave heating apparatus such as a microwave oven.
A microwave heating apparatus e.g. a microwave oven has usually an oven cavity containing an object being heated and a waveguide located on the outside of the upper wall (ceiling) of the oven cavity. One end of the waveguide is connected with a microwave inlet opening at the upper wall of the oven cavity, and the other end is connected with a magnetron which serves as a microwave emanating source. At the bottom portion of the oven cavity is provided a rack to put the object being heated such as food. In operation, a microwave is transmitted from the magnetron into the oven cavity through a waveguide and the object is heated.
In the oven thus constructed, the electromagnetic wave becomes a standing wave which causes the non-uniform heating of the object to be heated in it. In order to make a uniform heat pattern there are usually utilized some devices in which (a) an electromagnetic wave mode stirrer is installed on the oven ceiling for stirring the standing wave, by changing the reflection of the electromagnetic wave, or (b) a turntable is installed on the oven bottom for turning the object on it or (c) both stirrer and turntable are installed. However, these methods are not necessarily sufficient for good uniformity in heating, and furthermore, heating an object turned on a turntable in an oven cavity is sometimes inconvenient. There is a known method which has a stirrer in a waveguide coupling section and coaxially arranged with an electromagnetic wave mode stirrer in an oven cavity. The effect of this method is limited since the electromagnetic mode change is similar to that due to the complete synchronization between two stirrers.